In recent years, with regard to an inverter-driven electric vehicle, there has been known a battery-driven electric vehicle in which a power storage unit formed of a power storage device such as a battery is mounted, and electric power can be supplied from the power storage unit to an inverter that controls a motor for driving the wheels, so that the electric vehicle can travel even in a section where no overhead line is installed (for example, refer to Patent Document 1).
Recently, development of power storage devices such as a secondary battery and an electric double-layer capacitor has been being carried out actively, and the power storage amount has been enlarged; however, in order to obtain the electric-power amount large enough to make an electric vehicle travel, the current technology requires a considerably large and heavy power storage unit. In this regard however, because the mounting space in an electric vehicle is limited, it is required to suppress as much as possible the size and the mass of a power storage unit; thus, it is likely to difficult to ensure an ample power storage amount. Therefore, it is indispensable to effectively utilize limited storage power.
On the other hand, as an application example of electric vehicle that travels in a section where no overhead line is installed, for example, a suburban train has attracted attentions; by enabling an electric vehicle for a suburban train to travel by means of electric power from the power storage unit, overhead lines of part of the sections of an existing route can be removed, whereby overhead lines and support posts become unnecessary; therefore, the landscape is improved. In particular, in the route provided in the vicinity of a historic building or a scenic spot, the merit of removing the overhead lines and support posts is considerable in terms of the landscape. Moreover, in the case where an existing route is extended, only the lines may be extended without installing overhead lines, as long as the extension distance is not long; thus, there is produced a merit in which the construction costs can be reduced and the construction period can be shortened.
However, because sharing the travel path with an automobile, the suburban train is affected by a traffic jam or the like; therefore, the operational condition of the foregoing suburban train differs from that of an electric vehicle, on an ordinary rail-way route, that can travel in accordance with a predetermined time schedule, for example, in such a way that the travel time or the stoppage time in the section where no overhead line is installed is prolonged.
Accordingly, it is required that the capacity of the power storage unit is estimated with a margin, on the assumption that the travel time or the stoppage time in a section where no overhead line has been installed is prolonged; therefore, there exists a problem that a capacity larger than the capacity that is ordinarily required is necessary. Moreover, in the case where, due to a heavy traffic jam, an electric vehicle is forced to stop for a long time, the air conditioner (a cooling apparatus and a heating apparatus) mounted in the electric vehicle consumes electric power stored in the power storage unit, whereby the electric power becomes insufficient to make the electric vehicle travel, and then the electric vehicle cannot travel any longer; therefore, it is conceivable that the electric vehicle comes to a standstill in a section where no overhead line is installed.
Patent Document 1: Japanese Patent Application Laid-Open No. 2006-101698 (refer to FIG. 9 and Paragraph [0026])